Replace the compiling node.cpp/node.hpp skeleton with the full pool-layer
NodeImpl, ported near-mechanically from impl/ltc (namespace ltc -> dgb;
LevelDB net names litecoin -> digibyte). node.cpp now compiles share_tracker.hpp
and share_check.hpp into a real translation unit, exercising the chain-score path.

- node.hpp: BaseNode<dgb::Config, dgb::ShareChain, dgb::Peer>, async share
  downloader, tracker mutex/compute pipeline, broadcast, download, admin API.
  Config aggregator (core::Config<PoolConfig, CoinConfig>) declared inline since
  the dgb tree splits config into config_pool.hpp + config_coin.hpp (no
  config.hpp aggregator header).
- node.cpp: full run-loop body (think, clean_tracker, prune, PPLNS window,
  heartbeat, outbound connection maintenance, whitelist/ban admin).
- protocol_actual.cpp / protocol_legacy.cpp: per-message handlers (Actual/Legacy).
- config_pool.cpp / config_coin.cpp: Fileconfig load()/get_default() bodies;
  config_coin.hpp gains the YAML convert<> specializations for P2PData/RPCData.
- CMakeLists.txt: add dgb OBJECT lib (mirrors ltc lib) linking
  core/pool/sharechain/dgb_coin/btclibs/c2pool_storage/secp256k1; the dgb
  NodeImpl TU builds clean (target dgb).

Coin-isolation preserved: changes confined to src/impl/dgb/. Wiring the
c2pool-dgb executable to this lib requires edits in src/c2pool/ (main_dgb.cpp
+ CMakeLists.txt) which are out of scope for this slice.

The exe-wire slice repairs c2pool-dgb after #134 replaced the skeleton
node.cpp with the real abstract dgb::NodeImpl, orphaning the
run_skeleton/network_summary symbols the old stub main linked against.

main_dgb.cpp now drives the LIVE score path: it constructs dgb::ShareTracker
and calls score() (header-only, #132/#134), reporting the oracle block_period
(75s SSOT) the time_span derivation consumes. It never stands up the abstract
NodeImpl, so the full pool run-loop is not pulled in.

Isolation: the real node.cpp TU references core web_server/stratum, which the
core OBJECT lib links unconditionally and which drag in payout/merged/hashrate/
ltc (Phase B self-link tangle; merged = DOGE aux, NOT in the V36 default DGB
build). We therefore do NOT compile node.cpp into the exe and do NOT link core.
Instead we compile core/uint256.cpp directly and link the btclibs STATIC util
lib (HexStr/HexDigit) - pure utility, no pool runtime. Per-coin isolation held;
only the c2pool-dgb target changed; sibling coin exes still build.

Port of LTC whale_departure.hpp into the dgb namespace: 30-min rolling
hashrate window that detects whale departure (drop below 50% baseline)
and signals desired-target override toward pre_target3. Non-consensus,
local-only; matches p2pool-v36 work.py Phase 1c + 1c.1.

Compiled into the real node TU as an additive NodeImpl member; detect()
wiring into the desired-target path is the next slice. No shared-base or
src/core churn, single-tree under src/impl/dgb. c2pool-dgb builds clean.

…ride

Drive WhaleDepartureDetector::detect() from run_think() under the exclusive
tracker lock with the fresh best-share hash (race-free, share-batch cadence).
Publish the verdict to an atomic m_whale_departure_active and expose
local_desired_target(): when recovery is active the local mining target is
eased to pre_target3 (== MAX_TARGET, easiest consensus difficulty); otherwise
the normal desired target passes through. Non-consensus -- only affects what
this node mines, never share verification. Closes the loop on the pillar
landed in the prior slice (detector was dormant until it drove the override).

3-bucket: per-coin isolation (non-consensus local heuristic, src/impl/dgb/
only). redistribute.hpp deferred -- not a hard compile dep (comment-only
reference in share_check.hpp; file absent on branch).